In the mechanical power transmission field, gear-type shaft couplings have been used for many years for a wide variety of applications, including low, intermediate and high speed installations. This type of coupling is effective in adapting to misalignment between shafts in end-to-end relationship and will give optimum performance for long periods of time without substantial service other than maintaining proper lubrication between the sliding parts of the gearing in the coupling. One type of gear coupling usually used for high speed applications, consists essentially of a flange on each shaft with a spacer therebetween connected to the flange by splines; the teeth of the splines, normally being referred to as gears, are not contoured to permit substantial angular misalignment and parallel offset between the shafts, but, with the use of precision machining, they are particularly suitable for high speed operations. However, the precision machining and close tolerances enhance the production costs of the couplings. Another type of gear coupling, having gears on the periphery of the hubs meshing with internal gears of coaxial sleeves, has generally been difficult to install on the shaft initially and to service when replacement of the parts on which the gears are located is required. This often requires removal of the hubs from the shafts, reworking the shafts, and reassembling the parts of the sleeves containing the gears on the shafts before the hubs are assembled thereon. Since the hubs are often mounted onto the shafts by heating the hubs and then shrinking them onto the shafts, the preassembled gear sleeves are frequently subjected to sufficient heat to damage the seals in the sleeves. Further, if the gear sleeves require replacement, the hubs of this type of coupling must be removed before the gear sleeves can be removed and replaced, and in this servicing operation the replacement sleeves will be likely to be subjected to the heat required to secure the hubs to the shaft, thus subjecting the new sleeves to sufficient heat to damage the parts thereof, particularly the seals.
Another difficulty or problem frequently encountered in couplings used to connect shafts in an end-to-end relation, is the end play between the two shafts, or the end play of one shaft being transmitted to and causing end play in the other shaft. A related problem involves a condition in which one shaft is virtually free of end play during operation while the other shaft has a substantial amount of objectionable end play. With a number of couplings the construction is such that the axial stability of one shaft cannot be utilized to control the end play of the other. These various difficulties and problems have not, in the past, been eliminated or significantly minimized by the use of the standard or conventional gear couplings without substantial modification of the couplings.